The invention relates to a power-driven steady rest for lathes, especially crankshaft turning machines, which has a drive gear encompassing the workpiece to be machined, has a chuck for holding the workpiece, and is held on both sides adjacent the outer circumference by a bearing in a supporting plate fastened to the machine bed.
A lathe in the form of a crankshaft turning machine with a power-driven steady rest was disclosed in the manufacturer's brochure entitled "VDF Produktions-Kurbelwellen-Dreh-maschinen KD 1365" published in 1977. In machines of this kind a crankshaft is mounted in centers at its extremities for the machining of the main bearings and crank cheeks and is driven in rotation by means of a powered steady rest at the center of the crankshaft. The steady rest has a drive gear in which a chuck is disposed in which a crankpin of the crankshaft is placed, and transmits the drive torque to the crankshaft. The drive gear is supported on both sides by taper roller bearings of a conventional type. The outer race of the bearing is seated in a supporting plate screwed to the lathe bed, and the inner race rotates with the drive gear. On account of the very limited amount of space available, these bearings are very thin-walled, and their rotatory speed is limited by their large diameter. These bearings must withstand both radial and axial thrusts. The rotatory speeds that can be achieved with such bearings are too low, in the present state of the art, to achieve a very short machining time with modern carbide turning tools.
It is the object of the invention to improve the support of the drive gear of a power driven steady rest of this kind with regard to load bearing capacity and rotatory speed capability.